Benzene in Zeolite ZSM-5 Studied by Diffuse Reflectance Infrared Spectroscopy

Abstract

The behavior of benzene molecules in ZSM-5 has been studied in detail with the use of diffuse reflectance FT-IR spectroscopy. The infrared difference spectra indicate that benzene molecules have a high selectivity for adsorption first on the most energetic (Brönsted acid) ZSM-5 sites. The existence of at least two adsorbed benzene species has also been confirmed by infrared spectroscopy. Deuterated benzene (C₆D₆) species located at the ZSM-5 channels and channel intersections are characterized by the C-D stretching vibrations at 2284 and 2276 cm⁻¹, respectively. Since the high symmetry (D_6h) of the adsorbed benzene molecules is preserved, the framework of ZSM-5 may have been distorted. The distortion of the framework of ZSM-5 is also indicated by the red shift of the Si-O (or Al-O) asymmetric stretching vibrations (at ∼1215 cm⁻¹) when adsorbed benzene molecules are present.

Keywords

Benzene adsorption Zeolite ZSM-5 Diffuse reflectance infrared spectroscopy

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